In recent years, a variety of electronic devices including portable terminal devices, such as cell phones among others, have increasingly employed light emitting diodes (LED) or electroluminescence (EL) elements for illuminating their operating sections because these components allow the users to identify and operate push buttons or display sheets with ease in a dark environment. Touch panels and switches to be used in these devices thus need to be reliably operable and inexpensive.
A conventional touch panel and a switch are described hereinafter with reference to FIGS. 10 and 11. FIG. 10 shows a sectional view of the conventional switch, and its dimensions are enlarged thickness-wise for illustrating the structure more understandable. FIG. 11 shows an exploded perspective view of a conventional touch panel.
As shown in FIGS. 10 and 11, multiple lower electrodes 2 are arranged at predetermined intervals on a top face of film-like lower base sheet 1 of light transparency. Lower electrode 2 is belt-like and light transmissive, and made from indium tin oxide and the like. Multiple upper electrodes 4 are film-like and light transmissive, and arranged at predetermined intervals on film-like and light transparent upper base sheet 3 in a direction crossing with lower electrodes 2 at right angles. Upper electrode 4 is belt-like and light transmissive, and made from indium tin oxide and the like.
Upper base sheet 3 is layered on the top face of lower base sheet 1, and film-like light transparent protective sheet 5 is layered on the top face of upper base sheet 3. These sheets are bonded to each other with adhesive (not shown), so that touch panel 6 shown in FIG. 10 is constructed.
Multiple push-switches 8 are mounted on top face 7a of wired board 7, and upper end 8b of operating shaft 8a of switch 8 solidly touches underside 6a of touch panel 6. Multiple wiring patterns (not shown) are formed on top face 7a and underside 7b of wired board 7. Push switch 8 moves vertically its shaft 8a protruding upward for carrying out an electric contact.
Multiple light emitting elements 9, such as LEDs, are mounted on top face 7a of wired board 7, and they are placed between respective push switches 8 with their light emitting faces looking upward.
Light transparent and film-like display sheet 10 forms multiple display sections 10b at its underside. Light proof section 10a formed on the underside of sheet 10 by printing is punched to shape a letter or a symbol, thereby forming each one of display sections 10b. The switch is formed of display sheet 10 having display sections 10b placed above push switch 8, and wired board 7 including push switches 8 and light emitting elements 9 at its top face 7a, and touch panel 6.
Touch panel 6 to be used in the switch discussed above is generally manufactured through the following processes: First, lower base sheet 1 and upper base sheet 3, on which respective entire top faces conductive layers made from indium tin oxide and the like are formed, are covered with synthetic resin and the like at the places where lower electrodes 2 and upper electrodes 4 are to be formed, thereby providing each one of the foregoing places with a masking film. Then base sheets 1 and 3 are dipped into a predetermined solution for undergoing an etching process. Conductive layers except the masked places are melted and removed through the etching process before the masking film is peeled off. Base sheets 1 and 3 are then washed. Lower base sheet 1 having multiple lower electrodes 2 arranged at predetermined intervals on its top face is thus completed, and upper base sheet 3 having multiple upper electrodes 4 arranged at predetermined intervals at its top face and in the direction crossing lower electrodes 2 at right angles is also completed. Finally upper base sheet 3 is layered on the top face of lower base sheet 1, and protective sheet 5 is layered on the top face of upper base sheet 3, and these sheets are bonded together by adhesive, thereby completing touch panel 6.
The switch thus formed is mounted to an operating board of an electric device, and lower electrodes 2 as well as upper electrodes 4, multiple push switches 8, and light emitting elements 9 are coupled via wiring patterns or lead wires (not shown) to an electronic circuit (not shown) of the device.
The electronic circuit applies a voltage to multiple lower electrodes 2 and upper electrodes 4 sequentially, and a user lightly touches his/her finger to the top face of display sheet 10 for operating the device. Parts of electric charges of touch panel 6 travel to the finger, so that a capacitance between lower electrode 2 and upper electrode 4 touched with the finger changes, and then the electronic circuit can detect which part of display sheet 10 is touched and operated.
When display section 10b is pressed downward at a predetermined place, display sheet 10 and touch panel 6 are bowed downward, which depresses shaft 8a, and push-switch 8 carries out an electric contact. The electronic circuit thus detects which part of display section 10b is pressed for operating the device.
In response to the foregoing touch or press to touch panel 6, a variety of functions of the device is switched over, and the electronic circuit of the device supplies power to light emitting elements 9. Then multiple light emitting elements 9 emit light, and the light travels through touch panel 6 and illuminates multiple display sections 10b from below. This illumination from below allows the user to read a letter or a symbol on display section 10b even when the environment is dark, so that the user can operate the device with ease.
A change in capacitance of touch panel 6 prompts the electronic circuit to detect which part of display sheet 10 is touched and pressed with electric conduction through push switch 8. At the same time, multiple light emitting elements 9 emit light, so that multiple display sections 10b of display sheet 10 can be illuminated for the user to operate the device with ease.
Unexamined Japanese Patent Application Publication No. 2007-141269 is known as related art to the present invention.
Touch panel 6 and the switch using the same touch panel discussed above need a time consuming process for manufacturing base sheets 1 and 3, namely, base sheets 1 and 3 with multiple light-transmissive lower and upper electrodes 2 and 4 formed thereon are dipped in the solution for undergoing the etching process. This time consuming process inevitably increases the cost of the base sheets.